The present invention relates to disc drive systems and more particularly to a method and apparatus for burnishing asperities or irregularities from the surface of a disc.
In data processing systems, magnetic disc drives are used frequently as data storage devices. Data is written onto a rotating magnetic disc by an adjacent read-write head for later retrieval by the same head. The read-write head is located on a slider body, which is mounted to one end of a translatable arm that moves the head in a generally radial direction across the surface of the disc. As the disc spins, the read-write head flies above or below the surface of the disc, with the distance between the head and the surface of the disc depending on the rotational speed of the disc, the elastic force of the arm's suspension, and the shape and surface features of the slider body.
With the disc spinning at thousands of revolutions per minute (rpm), any unwanted interaction between the head and the disc surface can cause both short-term and long-term operational problems. This interaction can range from a thermal asperity to a full head crash. Consequences of contact or near-contact can include a failed read or write process, a temporary performance loss of the read-write head, a permanent defect on the disc surface, or total failure of the drive. These defects must be reduced or removed to provide sufficient clearance for the read-write head throughout the life of the product. Therefore, steps must be taken during the manufacturing process to flatten the disc surface as completely as possible, thereby improving product life and avoiding catastrophic head crashes. Typically, this is done by a burnish process after the disc media is fabricated.
During burnishing, the disc is rotated and the arm with the attached burnishing head is translated across the disc surface between an inner and outer diameter. The burnishing head is designed to fly close to the disc so as to physically contact defects protruding from the disc surface. The head is typically designed with burnishing pads and side rails on a contact surface projecting toward the disc to cut asperities and deflect loose particles as the disc rotates.
In combination with burnishing, a glide testing apparatus is also used to verify that the disc has been burnished sufficiently to meet quality and reliability requirements. The flying height of the glide head is typically lower than the operating height of the read-write head in the final product. The purpose of the lower flying height is to ensure removal of defects with the goal of improving quality and extending the useful life of the drive. A piezoelectric or thermal sensor or similar sensing means on the glide head is triggered each time that it encounters a defect on the surface. A control device electrically connected to the sensing means and the translator mechanism records the location of each defect in memory.
The distance between the disc and read-write head has necessarily decreased with advances in disc drive technology. The read-write head in modern disc drives flies nearly in contact with the disc at all times during normal operation. Therefore, to burnish each operative surface of the disc well below the design clearance of the read-write head, the burnishing methods and the burnishing head must also be improved to meet the increased demands of discs with higher data density.